U.S. patent application number 14/422775 was filed with the patent office on 2015-07-09 for elevator system using dynamic braking.
The applicant listed for this patent is OTIS ELEVATOR COMPANY. Invention is credited to Daryl J. Marvin, Kyle W. Rogers.
Application Number | 20150191327 14/422775 |
Document ID | / |
Family ID | 50150270 |
Filed Date | 2015-07-09 |
United States Patent
Application |
20150191327 |
Kind Code |
A1 |
Rogers; Kyle W. ; et
al. |
July 9, 2015 |
ELEVATOR SYSTEM USING DYNAMIC BRAKING
Abstract
An elevator system includes a motor having a plurality of motor
windings; a plurality of braking switches coupled to the motor
windings, the braking switches coupling the motor windings to a
common electrical point; a sensor coupled to the motor, the sensor
providing a sensed signal indicative of a parameter of the motor;
and a controller providing a braking signal to the braking switches
in response to the sensed signal to selectively control the braking
switches to short the motor windings.
Inventors: |
Rogers; Kyle W.; (Stamford,
CT) ; Marvin; Daryl J.; (Farmington, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OTIS ELEVATOR COMPANY |
Farmington |
CT |
US |
|
|
Family ID: |
50150270 |
Appl. No.: |
14/422775 |
Filed: |
August 22, 2012 |
PCT Filed: |
August 22, 2012 |
PCT NO: |
PCT/US2012/051837 |
371 Date: |
February 20, 2015 |
Current U.S.
Class: |
187/276 ;
318/379 |
Current CPC
Class: |
B66B 5/0043 20130101;
B66B 1/308 20130101; B66B 1/32 20130101; G01P 3/44 20130101; H02P
3/22 20130101; B66B 1/30 20130101 |
International
Class: |
B66B 1/30 20060101
B66B001/30; H02P 3/22 20060101 H02P003/22; B66B 5/00 20060101
B66B005/00; G01P 3/44 20060101 G01P003/44 |
Claims
1. A system comprising: a motor having a plurality of motor
windings; a plurality of braking switches coupled to the motor
windings, the braking switches coupling the motor windings to a
common electrical point; a sensor coupled to the motor, the sensor
providing a sensed signal indicative of a parameter of the motor;
and a controller providing a braking signal to the braking switches
in response to the sensed signal to selectively control the braking
switches to short the motor windings.
2. The system of claim 1 wherein the braking switches couple the
motor windings in a star configuration.
3. The system of claim 1 wherein the braking switches are
transistors.
4. The system of claim 3 wherein the braking switches are
MOSFETs.
5. The system of claim 1 wherein the sensed signal represents
current at the motor.
6. The system of claim 1 wherein the sensed signal represents speed
at the motor.
7. The system of claim 1 wherein the sensed signal represents
current and speed at the motor.
8. The system of claim 1 wherein the controller compares the sensed
signal to a threshold and generates the braking signal in response
to comparing the sensed signal to the threshold.
9. The system of claim 1 wherein the controller determines if the
elevator system is in maintenance mode, and provides the braking
signal only when the elevator system is in maintenance mode.
10. A method for providing dynamic braking in an elevator system,
the method comprising: sensing a parameter of a motor; determining
an operating mode of the elevator system; and selectively shorting
windings of the motor to a common electrical point in response to
sensing the parameter and determining the operating mode of the
elevator system.
11. The method of claim 10 wherein sensing the parameter of the
motor includes sensing current at the motor.
12. The method of claim 10 wherein sensing the parameter of the
motor includes sensing speed at the motor.
13. The method of claim 10 wherein sensing the parameter of the
motor includes sensing current at the motor and speed at the
motor.
14. The method of claim 10 further comprising: comparing the
parameter to a threshold and selectively shorting windings of the
motor to the common electrical point in response to comparing the
parameter to the threshold.
15. The elevator system of claim 10 wherein the controller
determines if the system is in maintenance mode, and provides the
braking signal only when the system is in maintenance mode.
16. An elevator system comprising: a motor having a plurality of
motor windings; a plurality of braking switches coupled to the
motor windings, the braking switches coupling the motor windings to
a common electrical point; and a controller providing a braking
signal to the braking switches in response to the system being in a
maintenance mode and a mechanical brake applied.
Description
BACKGROUND OF THE INVENTION
[0001] Embodiments of this invention generally relate to an
elevator system, and more particularly, to an elevator system that
employs dynamic braking.
[0002] Dynamic braking is a technique used to slow a motor through
the use of back electromotive force (emf). Generally, dynamic
braking operates by shorting terminals of a permanent magnetic
machine, allowing the back emf to resist rotation of the rotor.
Dynamic braking is used in a wide variety of applications.
Exemplary existing systems use switchover relays and power
resistors to connect motor leads together in a star connection.
This type of design is used in systems where a DC power source
remains charged at all times. Such systems require extremely high
cost relays to handle the currents generated by the active DC
source. Another exemplary existing design uses power resistors to
short the DC power source rather than the motor windings.
SUMMARY OF THE INVENTION
[0003] According to an exemplary embodiment an elevator system
includes a motor having a plurality of motor windings; a plurality
of braking switches coupled to the motor windings, the braking
switches coupling the motor windings to a common electrical point;
a sensor coupled to the motor, the sensor providing a sensed signal
indicative of a parameter of the motor; and a controller providing
a braking signal to the braking switches in response to the sensed
signal to selectively control the braking switches to short the
motor windings.
[0004] Alternatively, in this or other aspects, the braking
switches couple the motor windings in a star configuration.
[0005] Alternatively, in this or other aspects, the braking
switches are transistors.
[0006] Alternatively, in this or other aspects, the braking
switches are MOSFETs.
[0007] Alternatively, in this or other aspects, the sensed signal
represents current at the motor.
[0008] Alternatively, in this or other aspects, the sensed signal
represents speed at the motor.
[0009] Alternatively, in this or other aspects, the sensed signal
represents current and speed at the motor.
[0010] Alternatively, in this or other aspects, the controller
compares the sensed signal to a threshold and generates the braking
signal in response to comparing the sensed signal to the
threshold.
[0011] Alternatively, in this or other aspects, the controller
determines if the elevator system is in maintenance mode, and
provides the braking signal only when the elevator system is in
maintenance mode.
[0012] According to another exemplary embodiment, a method for
providing dynamic braking in an elevator system includes sensing a
parameter of a motor; determining an operating mode of the elevator
system; and selectively shorting windings of the motor to a common
electrical point in response to sensing the parameter and
determining the operating mode of the elevator system.
[0013] Alternatively, in this or other aspects, the parameter of
the motor includes sensing current at the motor.
[0014] Alternatively, in this or other aspects, sensing the
parameter of the motor includes sensing speed at the motor.
[0015] Alternatively, in this or other aspects, sensing the
parameter of the motor includes sensing current at the motor and
speed at the motor.
[0016] Alternatively, in this or other aspects, comparing the
parameter to a threshold and selectively shorting windings of the
motor to the common electrical point in response to comparing the
parameter to the threshold.
[0017] Alternatively, in this or other aspects, the controller
determines if the system is in maintenance mode, and provides the
braking signal only when the system is in maintenance mode.
[0018] According to another exemplary embodiment, an elevator
system includes a motor having a plurality of motor windings; a
plurality of braking switches coupled to the motor windings, the
braking switches coupling the motor windings to a common electrical
point; and a controller providing a braking signal to the braking
switches in response to the system being in a maintenance mode and
a mechanical brake applied.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The subject matter, which is regarded as the invention, is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features, and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0020] FIG. 1 illustrates an elevator system according to an
embodiment of the invention;
[0021] FIG. 2 is a schematic diagram of an exemplary system for
providing dynamic braking; and
[0022] FIG. 3 is a flowchart of an exemplary process for providing
dynamic braking.
[0023] The detailed description of the invention describes
exemplary embodiments of the invention, together with some of the
advantages and features thereof, by way of example with reference
to the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0024] FIG. 1 illustrates an example elevator system 10 including
an elevator car 12 coupled to one or more lifting and/or suspending
belts or ropes, generally referred to herein as belt 16. Belt 16
may be a coated, steel belt in embodiments of the invention.
Elevator car 12 is suspended or supported in a hoistway 14 with
belt 16. Belt 16 is routed around the various components of the
elevator system 10 by interacting with a traction sheave 18 and
idler sheaves 20, 22, 24. Belt 16 may also be connected to a
counterweight 26, which is used to help balance the elevator system
10 and reduce the difference in belt tension on both sides of the
traction sheave 18 during operation. Belt 16 supports the weight of
the car 12 and the counterweight 26 in a known manner.
[0025] Traction sheave 18 is driven by a machine 28. Movement of
traction sheave 18 by the machine 28 drives, moves and/or propels
(through traction) belt 16 to move car 12. The idler sheaves 20,
22, 24 are not driven by a machine 28, but help guide belt 16
around the various components of the elevator system 10. One or
more of the idler sheaves 20, 22, 24 may have a convex shape or
crown along its axis of rotation to assist in keeping belt 16
centered, or in a desired position, along the idler sheaves 20, 22,
24.
[0026] FIG. 2 is a schematic diagram of an exemplary system 100 for
providing dynamic braking to an elevator system. Dynamic braking
may be implemented when the elevator system is in a maintenance
mode, which is intended to include installation, maintenance,
inspection and upgrade, unless otherwise indicated. System 100
includes a motor 102, which may be part of machine 28 of FIG. 1.
Motor 102 is a multiphase machine having three motor windings 104,
106, and 108. Motor windings 104, 106, and 108 are coupled to phase
legs of an inverter 110.
[0027] Inverter 110 is power by a DC bus 112. As known in the art,
inverter 110 includes a number of switches 114. Switches 114 may be
MOSFETs, but other types of switches may be used, such as IGBTs,
IGCTs etc. Inverter 110 operates under the control of a controller
120. Controller 120 may be a general-purpose microprocessor based
controller, executing computer program code in a storage medium to
perform the operations described herein. Alternatively, controller
120 may be implemented in hardware (e.g., FPGA, ASIC) or a
combination of hardware/software. Controller 120 is coupled a gate
input of each of switches 114. By applying a drive signal to the
gate inputs, controller 120 turns switches 114 on and off to
provide an AC waveform to motor 102 and control the speed of motor
102.
[0028] System 100 also includes braking switches 130, 132 and 134.
Braking switches 130, 132 and 134 may be MOSFETs, but other types
of switches may be used, such as IGBTs, IGCTs etc. Braking switches
130, 132 and 134 connect motor windings 104, 106, and 108 in a star
configuration, effectively shorting the motor windings together at
a common electrical point. When the motor windings 104, 106, and
108 are shorted together, back emf of motor 102 provides a braking
force to the motor.
[0029] Controller 120 is coupled to a gate input of each of braking
switches 130, 132 and 134. By applying a braking signal to the gate
inputs, controller 120 turns switches 130, 132 and 134 on and off
to selectively short the motor windings. This allows controller 120
to control the braking force generated by motor 102. In an
exemplary embodiment, controller 120 use pulse width modulation
(PWM) to apply a pulsed braking signal to braking switches 130, 132
and 134. This pulsed braking signal selectively turns switches 130,
132 and 134 on and off, thereby selectively applying the braking
force at motor 102. It is understood that other braking signals may
be applied, and embodiments are not limited to PWM braking
signals.
[0030] System 100 also includes at least one sensor 140 that
provides a sensed signal to controller 120. Sensor 140 may sense
rotational speed of motor 102 and provide a sensed speed signal to
controller 120. Sensor 140 may sense current in the motor windings,
and provide a sensed current signal to controller 120.
Alternatively, both speed and current may be sensed at motor 120,
and a sensed speed signal a sensed current signal provide to
controller 120. Other parameters that indicate the operational
state of motor 102 may be sensed and provided to controller 120 in
the form of a sensed signal. As described herein, controller 120
uses the sensed signal to control braking signals applied to
braking switches 130, 132 and 134.
[0031] FIG. 3 is a flowchart of an exemplary process for providing
dynamic braking in the system of FIG. 2. The process is implemented
by controller 120. At 200, controller 120 detects the mode of
operation of the elevator system. The mode of operation may be
indicated by a group controller or master controller providing an
input to controller 120. If the mode of operation is not
maintenance mode, then at 202 the process loops back to 200.
Maintenance mode includes modes such as installation, maintenance,
inspection and upgrade of one or more components of the elevator
system.
[0032] If at 202 controller 120 determines the elevator system is
operating in a maintenance mode, flow proceeds to 204 where
controller 120 obtains the sensed signal from sensor 140. As noted
previously, the sensed signal may represent a plurality of
parameters, such as current in motor windings or rotational speed
of the motor 102. At 206, the sensed signal is compared to a
threshold to determine if dynamic braking is warranted. The
threshold may be set to allow some rotation of motor 102, or to
accommodate sensor tolerances. For example, a small amount of
current may be allowed to flow in the motor windings without
requiring braking. Similarly, some rotation of the motor may be
permitted in maintenance mode. The threshold may vary depending on
the desired operation of car 12. For example, car 12 is moved
during some maintenance tasks and the threshold may be defined to
allow movement of the car (e.g., up to a maximum speed) without
implementing dynamic braking. Thus, the threshold will vary
depending on the expected operation of the elevator system.
[0033] If the sensed signal does not exceed the applicable
threshold, flow proceeds to 208 where it is determined if the
elevator system is still in maintenance mode. If so, flow proceed
to 204 where the sensed signal is monitored. If not, flow proceeds
to 210 where the process ends.
[0034] If at 206, the sensed signal exceeds the threshold, flow
proceeds to 212 where dynamic braking is applied. This entails
applying the braking signal to braking switches 130, 132 and 134 to
selectively short motor windings 104, 106 and 108. This results in
braking of motor 102 due to back emf. While the system remains in
maintenance mode at 208, the process loops back through 204 and 206
to continually monitor the sensed signal and compare the sensed
signal to the threshold. This allows controller 120 to continually
adjust the braking signal in response to the sensed signal in a
feedback loop. For example, if the sensed signal increases in
magnitude, then the braking signal can be proportionally increased,
for example, with a larger pulse width. This process loop continues
until the system exits maintenance mode.
[0035] In an alternate embodiment, steps 204 and 206 are eliminated
and controller 120 proceeds directly to 212 when maintenance mode
is detected and instead of dynamic braking, a mechanical brake is
applied. This mode of operation removes the intelligent control of
steps 204 and 206 and provides a backup to the mechanical brake.
Since the braking signals are applied to braking switches 130, 132
and 134 upon entering maintenance mode, the dynamic braking is
present if the mechanical brake should fail.
[0036] The use of braking switches 130, 132 and 134 provides the
high current capabilities needed for a low voltage machine at a
much lower cost level than using relays. These braking switches
provide significantly increased lifetime over relays, as they are
designed to be switched millions of times. Additionally braking
switches 130, 132 and 134 require very little energy to be held in
a conducting state. By being able to control the braking switches,
it is possible to enable the switches only in maintenance mode,
thereby increasing the efficiency of the system. Braking force is
provided to motor 102 without disabling the upper and/or lower gate
drives 114 on the inverter 110. In systems that do not require
dynamic braking, switches 130, 132 and 134 can simply be
depopulated, removing the majority of the cost burden from the
drive.
[0037] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but defined by the scope of the appended claims.
* * * * *